This invention relates to marking techniques used to mark thin film magnetic media.
It is known in the magnetic disk manufacturing industry to provide manufacturing information about a particular product by printing the information on a surface of that product. This manufacturing information can include a product description, the lot number of that product, or the manufacturing facility where that product was produced, thereby enabling tracking or identification of the disk later in the manufacturing process or after shipment to the customer.
The manufacturing process of thin film magnetic disks, commonly used for storing data in computer hard drives, can be grouped into a series of primary steps. First, in the sizing and grinding step, a raw aluminum blank substrate is cut to proper dimensions and is ground to a desired flatness. Second, a nickel phosphorous (NiP) layer is formed atop the aluminum substrate. Third, the NiP layer is polished, textured, and cleaned. The disk is also laser textured. Fourth, in the sputter and lubrication (xe2x80x9clubexe2x80x9d) step, magnetic layers are deposited on the disk, covered by a protective overcoat, and a lubricant is applied. Finally, the completed disks are processed through a glide test and certification process.
FIG. 1 illustrates a cross-section of a finished magnetic disk 1 comprising an Al alloy substrate 2, a NiP alloy layer 3, a magnetic Co alloy layer 4, and a protective overcoat 5. A lubricating layer (not shown) is typically deposited onto the protective overcoat 5.
In the manufacturing of thin film magnetic disks, product marking has been accomplished by writing by hand the product information onto a portion of the surface of the disk. This crude method has several shortcomings. First, with the demand for increasing hard drive capacity, it is critical for manufacturers to be able to maximize the amount of surface area usable for storing data. A handwritten marking on a disk would render a substantial portion of the disk unusable for storing data, significantly reducing the value of that disk. Second, the manual step of writing on the disk is time-consuming and impractical for mass production of thin film disks. Thus, this method has been used primarily for marking experimental or test disks. Finally, the handling required for such a marking increases the likelihood of the disk being contaminated or damaged during the manufacturing process.
An alternative method for marking magnetic disks involves the use of a dedicated laser tool for printing alphanumeric characters on the surface of the disk. This marking step can be performed on a finished disk after the manufacturing process has been completed or on disks before the sputtering process. In either case, an additional step is added to the process, resulting in disadvantages similar to those described above. This method further requires the use of a specialized tool capable of laser-forming legible characters on the surface of the disk.
Alphanumeric laser marking has been accomplished by focusing a laser on the top surface of a finished or textured magnetic disk. The disk is held stationary, while a pulsed laser is positioned and focused to form visible deformations on the surface of the finished disk. The deformations are arranged such that they form visible alphanumeric characters. While this laser marking method may reduce the risk of damage or contamination of the disk by reducing the amount of manual handling of the disks required, it still necessitates the addition of another manufacturing step. In order for the characters to be legible, they must be made relatively large, thus reducing the amount of surface space available for storing data.
In accordance with the present invention, a method for marking a magnetic recording medium is provided. A marking zone is formed along a single track of a thin film disk using laser texturing. Product or manufacturing information is serialized on the surface of the disk in binary form, using long and short laser features to represent xe2x80x9conesxe2x80x9d and xe2x80x9czerosxe2x80x9d.
In one embodiment, the marking zone is formed as a ingle track along a radial, or circumferential, portion of the disk adjacent to the contact start-stop one (xe2x80x9cCSS zonexe2x80x9d). The laser features in the marking zone are formed during the same process and manufacturing step as the laser zone texturing (xe2x80x9cLZTxe2x80x9d) step for the CSS zone. This method enables marking of the disk without added tooling or manufacturing steps.
In another embodiment, the laser features in the marking zone are formed in an arc around a radial portion of the disk. A characteristic of the laser feature, such as the length of that arc, is visually identifiable and can be used as a simple method of quickly conveying information about the disk; longer arcs indicating, for example, one type of disk and shorter arcs indicating another.